The present invention relates to treatment of waste paper, waste paperboard or the like furnish to be recycled.
Due to the ecological and environmental considerations, the cost of virgin fibre and other factors, the optimizing of the recycling of waste paper etc. has now for some time been recognized as a very important aspect of papermaking technology.
One of the problems associated with paper recycling is the removal of print, coating or the like surface treatment to which the paper or cardboard may have been previously subjected. The removal of these components is subject of de-inking technology in paper making. The present invention is particularly, but not exclusively, directed to this field.
Industrial application of the presently available de-inking technologies is associated with relatively heavy use of de-inking chemicals which is expensive and environmentally undesirable. The known methods of deinking of waste paper or the like also require heavy use of cleaning and washing equipment which results in the requirement of a high investment capital. The demands for treatment water are also very high. Energy consumption associated with deinking and cleaning is also relatively high. And the presently available deinking technology has been shown to be inadequate for some furnished, so that the industry is not able to successfully reprocess all of the materials available.
Attempts have been made to alleviate at least some of the problems associated with the deinking of waste paper. For instance, in an article by H. Mamers. "The Siropulper--a new concept in wastepaper recovery" (APPITA, vol. 32, No. 2, pp. 124-128, September, 1978), the use of an explosive release digester is described for defibration purposes which may be used in de-inking. The article suggests that hydrodynamic forces of the explosive discharge combine with the chemical effects of the cooking process to release the ink particles from the fibres, reducing the chemical demand of the process. The increase of the pressure to achieve the required hydrodynamic conditions is effected by injecting pressurized inert gas into a reactor or digester.
The last mentioned method presents advance in that it contains the promise of reduced use of de-inking chemicals thus providing the potential for environmental improvement. The shortening of the processing period is another improvement over previous methods. Yet, certain disadvantages are still associated with this method. In particular, tests conducted in order to determine feasibility of the method described have shown that the quality of the final product of the method often does not reach the desired standard, particularly with respect to the appearance parameters of the final product.